This invention relates to burnable neutron absorbers and it has particular relationship to neutron absorbers in which the neutron-absorbing component or element is a boron compound. As disclosed in Radford-Carlson 1 and 2, the principal neutron-absorber boron compounds are boron carbide, B.sub.4 C, and zirconium boride ZrB.sub.2. The neutron absorbers are ceramic pellets including the boron compound in a matrix of a highly refractory material. The principle refractory materials are aluminum oxide, Al.sub.2 O.sub.3, and zirconium oxide, ZrO.sub.2. This invention has unique utility with respect of neutron-absorber ceramics in which B.sub.4 C and/or ZrB.sub.2 are encapsulated in a matrix of Al.sub.2 O.sub.3 and/or ZrO.sub.2. To the extent that this invention is applicable to neutron absorbers including other compounds of boron and/or other matrix materials, or in which the neutron-absorber elements are other than boron but manifest the same swelling properties as boron compounds, such application is within the scope of equivalents of this invention under the doctrine of equivalents as this doctrine is defined and explained by the U.S. Supreme Court in Graver Tank & Mfg. Co., Inc. et al. vs Linde Air Products Co. 339 U.S. Pat. No. 605; 70 S Ct 1017 (1950).
In the practice of the inventions disclosed in Radford-Carlson 1 and 2 satisfactory neutron-absorber ceramic pellets have on the whole been produced. However, at times, cracking or crumbling of such neutron-absorber pellets whose neutron-absorber element is a boron compound has been experienced. It is an object of this invention to overcome this drawback and to provide neutron-absorber pellets which can be relied upon not to crack or crumble.